This invention relates generally to air intakes for engines, and in particular to a barrier filter which protects an engine providing auxiliary power to an aircraft. An auxiliary power unit (APU) is a self-contained engine and generator system capable of producing electrical and/or pneumatic power for an aircraft, primarily while on the ground and typically while the main engines are not running. Although an APU can be mounted on a portable ground cart at an airport, it is more frequently mounted onboard the aircraft in an internal cavity. Typically, the cavity has tightly limited space constraints which restrict accessibility to perform maintenance tasks on the APU.
The APU requires intake air that is free from contaminants to provide for efficient combustion and avoid internal damage. The compressor and turbine are designed with small tolerances between moving parts which maximize efficiency, but which also increase vulnerability to damage from small contaminant particles. Contamination of intake air, even in a small amount, causes premature wear on engine components, increases maintenance costs, and degrades operational reliability. Unfortunately, aircraft are exposed to contaminants when operating at low altitudes where intake air is frequently contaminated with material from the ground, such as sand and dust. That problem is aggravated for helicopters due to rotor downwash and prolonged low-altitude operation.
The air inlet of many types of APUs is cylindrically shaped and covered with a mesh. It draws air from within the aircraft""s internal cavity over substantially an entire 360 degree periphery surrounding the APU for low pressure drop and highly efficient operation. It prevents large debris, such as leaves, from entering the engine. However, it is ineffective at blocking sand and dust. The position of the inlet in the limited space constraints of the internal cavity has prevented application of an effective filter or particle separating system. Such a system is difficult to install in a manner which seals around the inlet so that all incoming air is filtered, and which permits air to approach from substantially the full periphery for low pressure drop. Aggravating the difficulty is that the system must be accessible for installation, maintenance, and/or removal. Moreover, components of the APU, such as the accessory drive, oil pump, temperature sensors, fuel lines, and/or generator, form obstructions to freely installing or accessing any filter around the inlet.
Among the several objects and features of the present invention that may be noted the provision of an engine intake air filtration system which effectively removes contaminants; the provision of such a system which is usable in conjunction with an existing aircraft APU for installation in a cavity of tightly limited space constraints; the provision of such a system which draws air from substantially a full periphery around the APU; the provision of such a system which is readily accessible for maintenance; the provision of such a system which is adaptable to facilitate installation around various obstructions on the APU; the provision of such a system which is lightweight; and the provision of such a system which is economical.
In general, an air induction system of the present invention is for an engine to receive intake air from a region generally surrounding the engine, remove contaminants from the intake air, and provide the intake air for delivery to the engine. The engine includes a housing having an outer peripheral surface. The system comprises a filter formed of a filter media arranged in a generally annular shape for placement around a portion of the engine to receive intake air from the region generally surrounding the engine. A filter mount is engageable with the outer surface of the engine and configured for supporting the filter at an installed position wherein the filter is in spaced relation from the outer surface of the engine. The mount has an inner edge shaped and sized for sealingly engaging the engine and has an outer edge configured for sealingly engaging and supporting the filter.
In another aspect, a combination of the present invention includes an engine with an air induction system for protecting the engine from contaminant particles and which is readily installed or removed for facilitating rapid replacement such as for maintenance. The combination comprises an engine having a housing with an outer surface and a generally cylindric inlet. A filter formed of a filter media is arranged in a generally annular shape for placement around the inlet to receive intake air from the region generally surrounding the engine. The filter comprises at least two separable filter units. A filter mount is engageable with the engine and configured for supporting the filter at an installed position wherein the filter is spaced from the inlet. The mount has an inner edge shaped and sized for sealingly engaging the outer surface and having an outer edge configured for sealingly engaging and supporting the filter.
Other objects and features will be in part apparent and in part pointed out hereinafter.